Theft is baso if someone appropriates property belonging to another (actus reus) & is dishonest & an intent to permanently deprive (mens rea). Its all set out under S1 Theft Act 1968, and S2-6 provide definitions for each of those elements. Next are "(definitions) - key cases".
To add perspectives: Have you considered what can be deemed "criminal"? What "effect" can it be? Is "society" the same throughout the world? Does there exist almost a consensus on some level in every society on what is criminal (like murder, theft, etc)? Has your answer changed?
Think I've talked more about other stuff than about law itself hahaha. So here's some questions for my law class to answer (if we have time), from an Oxford interview I attended:
So thoughtful of my law teacher to invite me to her wedding with Brad Pitt on the day of my A-levels results day! Atleast I know there will be something to cheer me up, should the results not be those expected LOL